Second row captains chairs were available from at least 1994 (my RB E-350 came equipped with that and a flat folding bed) through 2009, I believe. My brother owned a 2004 7-passenger E-350 with this option in leather, but I think you could get them beyond then. They've changed slightly in style and seatbelt implementation over the years.
My EB is equipped with the so-call "quad captains chairs" option, making it a 14-passenger van. I'm sure they exist, but I've never seen another one. Most are the short vans. I seldom use any seats behind those 4.Tthe base for these seats is unique, so be sure to get them if you source the seats from a salvage yard. Seatbelts are unique too.
As for tie-downs, I use e-track right up to the back of the rear "captains charis". Watch the sheet metal screws when you secure track near the fuel tank. L-track is another option, but I've never used it. I've never had an issue with the e-track however.
2003 E-350 EB